The soil microbe bacillus thuringiensis (B.t.) produces a spore and a crystalline inclusion consisting of one or more insecticidal proteins referred to as .delta.-endotoxins. Preparations of the spores and crystals of B. thuringiensis subsp. kurstaki have been used for many years as commercial insecticides for insects of the order Lepidoptera. Recently, other species of B.t., namely israelensis and san diego, have been used commercially to control insects of the orders Diptera and Coleoptera, respectively (Gaertner, F. H. [1989] "Cellular Delivery Systems for Insecticidal Proteins: Living and Non-Living Microorganisms," in Controlled Delivery of Crop Protection Agents, R. M. Wilkins, ed., Taylor and Francis, in press). In addition, with the use of genetic engineering techniques, new approaches for delivering B.t. endotoxins to agricultural environments are under development, including the use of plants genetically engineered with endotoxin genes for insect resistance and the use of stabilized intact microbial cells as B.t. endotoxin delivery vehicles (Gaertner, F. H. and L. Kim [1988] TIBTECH 6:S4-S7). Thus, isolated B.t. endotoxin genes are becoming commercially valuable.
Recently, many new subspecies of B.t. have been identified, and many genes responsible for active .delta.-endotoxin proteins have been isolated (Hofte, H., and H. R. Whitely [1989] Microbiological Reviews 242-255). Thus, many different B.t. toxins are now known. However, to date, the method for isolating the responsible toxin genes has been a slow empirical process. That is, for a given B.t. isolate, there is currently no rapid systematic method for identifying the responsible toxin genes or for predicting the activity of a given B.t. isolate, Currently, a given B.t. isolate must first be placed through a tedious series of bioassays to determine its spectrum of insecticidal activity, and subsequently an attempt is made to isolate the genes responsible for the observed insecticidal activity, generally through the nonsystematic use of mixed or randomly selected oligomeric probes.
The subject invention eliminates much of the empirical nature of finding new B.t. insecticidal protein toxin genes. This invention places the systematic isolation of novel B.t. insecticidal toxin genes and their associated .delta.-endotoxins within reach of the practitioner in the insect-control art and, also, enables a rapid early identification of potentially new commercially valuable insecticidal endotoxin genes.